Opera site served Blackhole malvertising, says antivirus firm

Opera has suspended ad-serving on its portal as a precaution while it investigates reports that surfers were being exposed to malware simply by visiting the Norwegian browser firm's home page.

Malicious scripts loaded by portal.opera.com were redirecting users towards a malicious site hosting the notorious BlackHole exploit kit, said a Romanian anti-virus firm BitDefender, which said it had detected the apparent attack on its automated systems. BitDefender said it promptly warned Opera after it detected the problem on Wednesday. It seems likely the scripts had been loaded through a third-party advertisement, a practice commonly known as malvertising.

Opera has yet to confirm the problem, but has disabled advertising scripts on its portal in case they are tainted. The browser firm says:

We are investigating the claim, and while we are working with this, we have taken some precautionary measures just to be safe, such as disabling the ads temporarily on portal.opera.com. We disabled ads yesterday [Wednesday], right after becoming aware of the claim, as a standard precaution and the ads had been disabled for several hours when Bitdefender issued a press release.

A blog post by BitDefender claimed that cybercrooks were using obfuscated script to hide the attack. The security firm said Opera fans had been exposed to attack simply by firing up the popular alternative browser software.

"The hidden and obfuscated piece of code in the Opera Portal homepage inserts an iFrame that loads malicious content from an external source," BitDefender explains. "If the Opera user hasn’t changed their default homepage, active malicious content is loaded from a third-party website whenever they open their browser."

In controlled tests, BitDefender researchers were served with a PDF-based exploit designed to infect an unlucky user with a freshly compiled variant of the infamous ZBot (ZeuS) banking Trojan. The exploit was served up from a (likely compromised) server in Russia, according to BitDefender. It's unclear how many people might have been exposed to this drive-by-download-style attack from Opera's portal, much less how many surfers might have been infected.

"We have no indications that anyone was infected before or after we disabled the ads yesterday [Wednesday]," an Opera spokesman told El Reg.

"Malvertising" incidents are far from rare. Previous victims have included Spotify, the London Stock Exchange, The Pirate Bay, ITV.com and Major League Baseball, among many others. Diagnosing and resolving tainted ad problems tends to be far trickier than cases where a web server itself is running malicious script, so Opera is wise to suspend ad-serving while it looks into the potential problem. ®